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Biologist Firmly Planted in High-Level Research at Bowdoin

Story posted May 26, 2006

This is a story about science. Pure, basic science conducted for the challenge of understanding more about our world.

This is the story of scientist Bruce Kohorn - a plant-cell biologist who left a major research institution because he believed Bowdoin would be a better environment for doing his research while still teaching.

Bruce Kohorn

This is also a tale of an accidental discovery that put Kohorn and his colleagues in the forefront of plant-cell research.

It all begins with a mustard-plant cell.

In 1996, Kohorn was an established researcher at Duke University, and one of several thousand scientists worldwide working on one of the basic questions of plant biology: What molecules determine plant-cell shape or size?

At the most basic level, says Kohorn, shape and size can only come about in two ways: "One is cell division," he says. "The frequency at which cells divide and make copies of themselves will dictate the number of cells and their size.

"There is another factor," he adds "and that's regulation. How does a cell actually enlarge once it divides? There is no one answer, but thousands of ways it can be controlled. It's a question scientists have been trying to understand for a long time."

While Kohorn and his colleagues were studying another aspect of plant-cell growth - photosynthesis - they stumbled upon an unusual protein in the mustard plant Arabidopsis. It had parts inside, as well as outside the cell, embedded in the cell wall. Those inside the cytoplasm were kinases - proteins that can relay signals from one place to another.

A diagram of a WAK, left, shows how pectin, a flexible part of the cell wall, may activate the kinase inside the cell to increase sugars, causing cell expansion. On the right is an actual confocal image of the protoplast expressing WAK in green, Vacuole marker in red, chlorophyll in blue.

"When we saw this protein that spanned the membrane, had something sticking outside into the supporting cell wall, and also a kinase inside, we said, 'It really might be something that allows a molecule to signal from outside the cell wall to the inside.' We realized that through sheer serendipity, we had identified a protein that may well be regulating cell expansion," says Kohorn. "It was pretty exciting."

They called this new receptor protein Wall Associated Kinases, or WAKs. They published their findings in The Plant Cell, Journal of Biological Chemistry, and Plant Molecular Biology, where they sent ripples through the scientific community.

Student-Fueled Research

Jason Lewis '06, left, and Sarita Fu '06 in the lab with Kohorn.

"I have two goals," says Kohorn, ambling into his laboratory on a spring afternoon. "One is to make progress in my research, and the other is to teach and get students excited about science."

Two such enthusiasts are already there, Jason Lewis '06 and Sarita Fu '06.

Sarita has worked in Kohorn's lab since her sophomore year, including summers. Working side-by-side with him at the bench, Fu says she has had the gratification of experiencing first hand "how students can actually contribute to real science."

Sarita and Jason were links in a chain of lab work and research that resulted in Kohorn's recent article in The Plant Journal, which he co-authored with Nicole Byers '05, Anjali Dotson '05, and Jeff Riese '02.

"I love working at the bench, peering down the microscope, and teaching the students how to do research," says Kohorn. "I start them out doing smaller tasks, but usually they are so good they catch on fast and learn how to become independent."

"When you consider who he is, it's a little intimidating," giggles Fu. "But when he's trying to teach you how to do something, he'll take you step-by-step. He's really into you learning it."

Then Kohorn did something that may have caused even more ripples in the scientific community. In 2001, he left Duke to come to Bowdoin.

"I wanted to be in a place where I could work at the lab bench myself and concentrate on science for the sake of science," says Kohorn. "I think society is forgetting the importance of basic science and has now become far more directed toward a product.

"I love it at Bowdoin. The undergraduates I have working in my lab are a diverse and interesting group. They come in with an open mind, and when they leave are even more excited about science and their future. I find this very refreshing."

One of the first things Kohorn did at Bowdoin was to win a major National Science Foundation grant that, among other things, allowed him to purchase a confocal scanning laser microscope. The highly sophisticated equipment lets him get high-resolution, three-dimensional fluorescent images from both live and fixed samples. It is being used by several departments within the College, by faculty members at the University of New Hampshire, and is available to other Maine institutions.

The microscope will also aid him in the next stages of his research on WAKs. After several studies in which he and his co-authors confirmed the function of WAKs in cell-wall expansion - which they published in Plant Journal and The Journal of Cell Science - Kohorn has fine-tuned his inquiries. He is now trying to understand how the cell wall communicates with the rest of the cell.

How does a cell control the extent of expansion? How does the inside of a cell know its outside wall is expanding?

Kohorn suspects these changes occur, in part, due to the movement of pectin - which is a flexible part of the cell wall. In one model, Kohorn posits that pectin activates the kinase inside the cell to increase sugars, which then increase the amount of water in the cell. Thus, the cell expands.

"I wanted to be in a place where I could work at the lab bench myself and concentrate on science for the sake of science."

"If you don't have a WAK outside the cell wall, you won't expand," suggests Kohorn. "You'll be a dwarf cell. I think it's pretty fundamental. "

Naturally, one basic question leads to another.

Kohorn is now investigating pectins more deeply. "I'm fascinated by how the pectin is activating this protein," he says. "In new experiments, which I'm working on with several student-researchers, we are taking cells that have WAKs and stripping away the cell wall where the pectins are located. When we add back a mix of pectins, the WAKs become activated. So, now we're asking, 'What kind of pectin is doing this?'"

"I was fortunate enough to work with Prof. Kohorn for long enough that I got to see my work used as evidence and published in a major journal," says Sarita Fu, a biochemistry major. "That was pretty neat."

Ultimately, Kohorn hopes to develop a three-dimensional picture of the structure of the actual protein down to its individual atoms. It would be a remarkable accomplishment: No one yet knows how proteins bind pectin.

"Pectin is ubiquitous in plants," says Kohorn. "If you can understand its structure, you can open up a lot of discussion.

"Plus," he adds, grinning, "pectin is important in other ways. It's used as a thickener for everything from toothpaste to ice cream. And where would we be without those?"